1. Field of the Invention
The present invention relates to an improved process for producing trans-[hydridocarbonyl tris(triorganic phosphine) rhodium (I)] [RhH(CO)(PR.sub.3).sub.3 ] (wherein R represents an organic group such as phenyl, alkyl, aryl, alkoxy and aryloxy group) by reducing trans[chlorocarbonyl bis(triorganic phosphine) rhodium (I)] [RhCl(CO)(PR.sub.3).sub.2 ] with tetrahydroborate in the presence of a triorganic phosphine (PR.sub.3) in a solvent.
2. Description of the Prior Arts
Recently, rhodium complexes especially RhH(CO)(PR.sub.3).sub.3 (PR.sub.3 : triorganic phosphine) have been used as catalysts for a hydroformylation of an olefin, an isomerization and a hydrogenation in various fields. These compounds have been usually produced by using RhCl(CO)(PR.sub.3).sub.2 as a starting material. In accordance with the conventional processes for producing RhH(CO)(PR.sub.3).sub.3 from RhCl(CO)(PR.sub.3).sub.2, however, a yield of the product is low and the product contains an impurity to be a low purity. It has been needed to overcome these disadvantages. Moreover, rhodium metal is remarkably expensive and accordingly, it is quite important to obtain these complexes having high purity at high yield from the economical viewpoint. It has been needed to develop an advantageous industrial process.
In the conventional process for producing RhH(CO)(PR.sub.3).sub.3 from RhCl(CO)(PR.sub.3).sub.2, an ethanol solution of trans-[chlorocarbonyl bis(triphenyl phosphine) rhodium (I)] [RhCl(CO)(PRh.sub.3).sub.2 ] and triphenylphosphine (PPh.sub.3) is refluxed in nitrogen gas atmosphere and then, an ethanol solution of sodium tetrahydroborate was added, to react them and the reaction mixture is separated by a hot filtration to obtain the object compound (Shin Jikken Kagaku Koza Vol. 12 Page 198 (1976) Maruzen). In accordance with the proposed process, the resulting trans-[hydridocarbonyl tris(triphenyl phosphine) rhodium (I)] [RhH(CO)(PPh.sub.3).sub.3 ] has a low purity and contains an impurity and are not advantageous, in an industrial use as a catalyst.
In the other conventional process, an ethanol solution of rhodium (III) chloride trihydrate is added dropwise to an ethanol solution of triphenyl phosphine under refluxing the mixture and then, an aqueous solution of formaldehyde and an ethanol solution of tetrahydroborate are added to the mixture to obtain the product (J. Chem. Soc. (A) 1968 Page 2664). In accordance with the proposed process, a purity of the product is low and an yield of the product is low so that a collection step and a recovery step for rhodium are needed since rhodium is expensive. Therefore, this process is not advantageous as an industrial process.
When the product of RhH(CO)(PR.sub.3).sub.3 having a low purity obtained by said process, is used with PR.sub.3 and a water miscible organic solvent in a hydroformylation of an olefin, a layer of an insoluble by-product contained in the complex (an interface material) is formed between the organic solvent layer and the water layer in a step of an extraction of the reaction product with water. Therefore, an extraction in the hydroformylation is not easily attained and a loss of the expensive rhodium component is caused. When the reduction and the cooling step are carried out in a nitrogen atmosphere, an yield of the rhodium product is not high enough. The present invention has been attained by increasing the yield of the rhodium product.